Introduction

Fertilisation in the brown alga Fucus involves species-specific interactions between biflagellate sperm and spherical eggs (Bolwell et al., 1977; Evans, Callow & Callow, 1982; Callow, Callow & Evans, 1985; Callow, Stafford & Green, 1992). We are interested in two related aspects of Fucus gamete cell surfaces: 1) How are the cell surface molecules organised? and 2) What is the molecular basis of recognition and the associated cell responses that occur within a few seconds or minutes of gamete fusion? Such studies in higher plants are difficult because the gametes are embedded within tissues, and plasma membrane based receptors have limited accessibility because of intervening cell walls. In addition, it is still relatively difficult to obtain gametes in sufficient numbers from higher plants compared with Fucus from which naked gametes are released in large enough quantities to allow detailed biochemical studies (Bolwell, Callow & Evans, 1980; Stafford, Callow & Green, 1992a). Thus the Fucus system has much to offer, and hopefully the findings will be relevant to gamete interactions in higher plants. This review will focus on how we have used a combination of biochemical and immunological approaches to study: 1) the organisation of the Fucus egg cell surface and 2) the role of sperm proteins in egg binding and the triggering of cell wall release.